Process of treating ores containing galena



N. C. CHRISTENSEN. PROCESS OF TREATING ORES CONTAINING GALENA.

APPLICATION FILED APR.9, 1920.

Patented. 00 31, 1922 Patented ct. 3i, l922.

NIELS C. CHRISTENSEN, 0F SALT LAKE CITY, UTAH.

PROCESS OF TREATING @RES CONTAINING GALENA.

Original application filed September 30, 1919, Serial No. 327,401.

Divided and this application filed April 9, 1920. Serial No. 372,689.

To all whom it may concern:

Be it known that I, NIELs C. CHRISTEN- SEN, a citizen of the UnitedStates, residing at Salt Lake City, in the county of Salt Lake and Stateof Utah, have invented cer-' tain new and useful Processes of TreatingOres Containing Galena, of which the following is a specification.

This invention relates to the treatment of ores containing galena forthe recovery of the lead and silver therefrom. My process is applicableto all galena ores which do not contain too much readily solublematerial such as calcite. It recovers practically all the lead andsilver in the galena and also the silver not held by the galena if it isin the form of sulphide or antimonide. The sulphur of the galena is alsorecovered in a form which is readily handled.

My process consists in treating the finely ground galena with aconcentrated salt solution containing ferric chloride. I have found thata relatively concentrated solution of sodium chloride or calciumchloride containing ferric chloride acts on the galena, dissolving thelead and silver and freeing the sulphur. The cold solution acts slowlyand holds a comparatively small amount of lead but a hot solution actsvery rapidly and holds a relatively large amount of lead. The lead andsilver go into solution as chlorides and the sulphur is separated asfree sulphur. The reaction is indicated below:

As shown by FeCl -l-ClzFeCl,

I bring about this change from ferrous to ferric iron by electrolyzingthe lead chloride to secure lead and chlorine. and using this chlorineto change the iron from ferrous to ferric chloride. This may be done byelectrolyzing the molten lbCl and passing the chlorine into the ferrouschloride solution or by electrolyzing the PbCl in the salt solution, theferrous iron being changed to ferric at the anode. This operation shouldpreferably be carried out in a cell with a diapliragm between the anodeand cathode compartments to prevent the reduction of the ferric iron tothe ferrous condition at the cathode. The lead chloride is added to thecathode compartment and the ferrous chloride solution to the anodecompartment and the lead removed as lead sponge and the ferrous solutionchanged to ferric.

Either ferric chloride or ferric sulphate may be used as the ferricsulphate is changed to the chloride in the salt solution.

The hot salt solution holds a great deal more lead in solution than thecold solution, and in my preferred method of treatment I take advantageof this to separate the lead chloride from solution, the ore beingtreated with a hot solution to dissolve the galena, and this hotsolution then separated from the ore and cooled, and the precipitatedlead chloride separated from the cold solution. The difference insolubility of the lead chloride in the hot and cold solution isindicated by the curve in my patent application No. 327,400 also on thetreatment of galena ores.

My preferred method of carrying out my process is as follows: Thecomminuted ore is agitated for from a short time (from 10-30 minutes ormore according to the fineness of grinding, etc.) with hot salt solutioncontaining over the amount required to react with the lead (and silver)sulphide according to the chemical equations given above. I have alsofound it advantageous to use a small amount of acid with the ferricchloride in order to reduce the hydrolysis of the ferric chloride. Thistreatment brings the lead (and silver) into solution. This hot pregnantsolution is then separated from the ore (preferably by filtration) andcooled and the precipitated lead chloride separated from the coldsolution. This lead chloride is then electrolyzed and the chlorine usedto convert the ferrous into ferric iron so that the solution may be usedfor the treatement of more ore. This electrolysis may be carried out bymelting the lbLl and electrolyzing it, giving melted lead and chlorine.The chlorine is then absorbed by the ferrous salt solution in anysuitablev absorption apparatus. It is adyantageous to have some saltpresent with the molten lead chloride in order to reduce the meltingvpoint and lower the resistance of the molten bath.

The lead chloride may also be electrolyzed in a concentrated saltsolution, the lead being precipitated as a sponge and the chlorinechanging the ferrous iron to ferric at the anode. The electrolysisshould preferably be conducted in a cell with a diaphragm to prevent thereduction of the ferric chloride at the cathode. A comparatively low E.M. F. may be used in this electrolysis as the reactions at the anodegive back a considerable portion of the energy used at the cathode.Theoretically the voltage should be approximately one-half volt, butthis cannot of course be realized'in practice due to the resistance ofthe solution and diaphragm. My preferred method of carrying out theelectrolysis in the solution is to electrolyze the warm solutioncontaining the lead in a cell with a porous diaphragm. The pregnantsolution is allowed to flow into the cathode compartment Where the leadis deposited, and then into the anode compartment where the ferrouschloride is changed to ferric chloride and the ferric solution then usedto treat more galena ore.

In the annexed drawings 1 have shown various forms of apparatusapplicable to the steps of my process, in which,-

Fig. l is a general diagrammatic view of the method and an apparatus bywhich the process may be practiced;

Figs. 2, 3 and 4, are views showing an apparatus employed for heatingand cooling the solutions and for the absorption of the chlorine; and

Figs. 5 and 6 are views illustrating a modified form of the apparatus.

Referring to Fig. 1, the full line 0 indicates the comminuted ore; thedot and dash line P the pulp (mixture of solution and ore); the brokenline S the solution; the broken line TV the wash water; the broken lineW. S., the wash solution; the dotted line Cl. the chlorine; the fullline PbCl the lead chloride; the full line Pb the lead bullion. Theapparatus shown consists of a series of small mechanical agitators 1preferably made of porcelain or acid proof earthenware; a filter 2 madeof similar acid proof material and using tubes of porous alundum as thefiltering medium (tubes of filtros or porous porcelain, etc., may beused but I have found the alundum tubes 2. very excellent filteringmedium for this work). A reducing tank 3 made of porcelain orearthenware; a precipitating tank 4, preferably made of acid proof tileof the Zinc box type used in cyanide and copper precipitation work: a.cooler 5. consistin of a. special form of air cooler described later.The cooler may be made of wood Q0 struca insane? "tion if desired as thesolutions coming from the precipitator or in a reduced condition and notas corrosive, as in the earlier stages of the process; a settling tank 6which may also be of wooden construction; an electro lytic furnace 7suitable for the electrolysis of the molten PbCl a special absorptionapparatus 8 for the absorption of the C1 in the mill solution, of acidproof tile or wooden construction, described later; a special heatingdevice 9 for heating the mill solution by direct contact with hot gases.The special pieces of apparatus, 5, 8, 9, for heating and cooling thesolutions and for absorbing the chlorine are constructed on the samegeneral principle. The general method of construction is indicated inFigs. 2, 3, 4: and The method of handling the solutions in each of theseis as follows:

The solution is made into a spray by bringing the surface of a rapidlyrevolving ,cylinder 10 into contact with the surface 111 of the solutionso that the cylinder dips slightly into the liquid (from to according tothe density of the spray desired). This operation is conducted in anenclosed passage surrounded by a suitable housing 12, in the lower partof which the solution is contained and the upper part 13 of which isfilled with the spray thrown by 9 the cylinder 1. The gases to bebrought into contact with the spray of solution are passed through thespray enclosed in the housing 12. For example, for heating the solution,hot gases from a furnace or stoveare passed through the spray; forcooling the solution, cold air .is passed through the spray,'cooling. itby evaporation; for the absorption of chlorine or acid gases, thesegases are passed through the spray. For acid absorption and to securethe highest efficiency in heating and coolin a counter current flow ofgases and solution is preferable. This counter current fiow is securedby passing the gases and solution through the tunnel or housing 12 inopposite directions, as shown in Figs. 2, 3 and 4-.

Fig. 2 shows a longitudinal vertical sec tion of the apparatus and Figs.3 and 4 vertical cross sections showing different shapes of housing. Thecircular housing 12 shown in Fig. 3 does not obtain the benefit of thefull fan of spray thrown by the cylinder, whereas the fan shaped housing12 of Fig. 4c secures the benefit of a larger part of the fan of spray.This type of housing is also especially suitable for construction ofacid proof brick. The choice of the style of housing will depend on thevolume of gas to be handled and the material of construction, a numberof sections of housing may be connected in series to secure as long aperiod of contact between gases and solution as is desired. In this casethe flow of gases and the flow of solut on are para l l to the axis ofthe cylinder spray 1, but in opposite directions, the gases entering at14.

and leaving at 15 and the solutions entering at 16 and leaving at 17.

For cases in which it is not desired to secure such an efficient countercurrent, as just described, the arrangement shown in Figs. 5 and 6 maybe used. Fig. 5 shows a vertical section of one of the housings of thisapparatus, which is similar to that shown in Fig. 4 except that thegases in this case pass through the housing 12 and spray transversely tothe axis entering at one side 18 and leaving at the other 19. In orderto secure a counter current effect in this type of apparatus a number ofsuch sections of housing are placed side by side so that the cylindersare end to end, and the gases flow through successively, through thehousings as shown in Fig. 5, which is a plan view of this arrangement,as shown by the arrows 20 entering at 18 and leaving at 19. The solutionenters at 21 and flows through each housing parallel to the axis of thecylinders 1 leaving at 22. This arrangement of my apparatus has someadvantages in construction for Work with acid solutions.

The process is carried out in a general Way as follows: The hot saltsolution 3 contain ing the ferric chloride and the cornminuted (O) oreare continuously fed into the first of the series of agitators 1, insuitable relative proportions and passed through the agitators to thefilter 2 where the hot pregnant solution is removed and the residue ofore washed with the wash water From the filter 2 the pregnant solutionpasses through the reducing box 3 which contains galena. (or lead ifdesired), sufficient time being allowed in this box to reduce the excessof ferric chloride remaining in the solution. From the reducer 3 the hotpregnant solution flows to the precipitation box 4 in which the gold andsilver are first precipitated with copper (or lead, if desired) and thecopper with lead. From this precipitator the hot solution flows to thecooler 5, bein first mixed with the wash solution from the filter tocool and dilute the solution so as to secure as complete a precipitationas possible. In passing through the cooler the solution is cooled by acurrent of cold air blown through the spray of solution, as previouslydescribed. This results in a considerable evaporation of water from.thesolution. The cold solution carrying the precipitated PbCl flows to thesettling tank 6 and the lead chloride is settled out. The lead chlorideis dried and electrolyzed in a molten condition in the electrolyticfurnace 7 giving molten lead and chlorine. The chlorine (C) is absorbedin the cold barren mill solution in the absorber 8 by being brought intocontact with the solution spray. as previously described, converting theferrous chloride to ferric chloride. From the absorber 8 the solution ispassed through the heater 9 and is heated by bringing the solution sprayinto contact with hot gases from a furnace or grate, as previouslydescribed. The position of the absorber 8 and heater 9 may be reversed,if desired, absorbing the hot chlorine from the electric furnace 7 inthe hot solution. The heating of the solution with the hot gases in theheater 9'results in a considerable evaporation of water from thesolution. As previously stated this loss is made up by the wash waterused in washing the lixiviated ore.

The tailings-(T) discharged from the filter 2 may be treated by theflotation process to recover any pyrite or chalcopyrite which maycontain gold and silver.

Though the apparatus described disclose my preferred forms, others maybe used, if desired.

From the foregoing it will be apparent that the process is subject tomany variations in the details of the manner of its application, butthat the main features of the process are, first, the dissolving of thegalena in a hot salt solution containing ferric chloride whereby theferric chloride is reduced to ferrous chloride, and second, theelectrolysis of the lead chloride to get lead and chlorine and the useof this chlorine to convert the ferrous chloride to ferric chloride sothat the latter may be used in the treatment of more ore.

By my process it is possible to make a practically complete recovery ofthe lead and sulphur and silver and gold, and in many cases the copper,from galena ores. In the process the silver and gold ispreferablyprecipitated, first, with copper, the copper with lead, and the lead byone of the methods previously described. In most ores all the gold andsilver and copper, except that which is locked up in the pyrite 0rchalcopyrite which is present in the ore are easily recovered by myprocess.

As before mentioned the many variations in the details of methods ofapplication of the process are. too numerous to be given in the scope ofa patent application, and do not therefore desire to be limited'by thebrief descriptions given, but by the appendlead chloride therefrom, andelectrolyzing the said lead chloride to recover the metallic lead andchlorine therefrom and adding said chlorine to the solution Which hasbeen reduced by above said treatment and thereby changing the ferrousiron to the ferric condition in said solution and using said solution inthe treatment of more ore.

In testimony whereof I have signed my name to this specification.

NIELS C. CHRISTENSEN.

